Hybrid fiber-coaxial (HFC) is a broadband network, which combines a fiber optic network and a coaxial cable network. The fiber optic network may extend from a cable operators' headend to a fiber optic node, which serves anywhere from 25 to 2000 customer premises. In downstream communication to customer premises, the headend may obtain downstream data via satellite dishes or other sources of information and optically transmit the downstream data over an optical fiber of the fiber optic network to a fiber optic node. The fiber optic node in turn converts the optical signals received from the headend into electrical signals and transmits the electrical signals to the customer premises via coaxial cables. In upstream communication from a customer premise to the fiber optic node, the customer premise sends upstream signals over a coaxial cable to the fiber optic node, which in turn converts the upstream signals into optical signals and transmits the optical signals to the headend.
In performing upstream communication from a customer premise to a fiber optic node over the coax, a frequency range between 5 mega hertz (MHz) and 42 MHz (or a frequency range between 5 MHz and 65 MHz in Europe or a frequency range between 5 MHz and 85 MHz as specified for DOCSIS 3.0 systems) has been generally allowed for the upstream communication. In performing downstream communication from a fiber optic node to customer premises over the coax, a frequency range with the lower end of 50 MHz and the upper end ranging from 750 MHz to 1000 MHz has been generally allowed for the downstream communication. Because the frequency range for upstream communication is bounded at the upper end by the downstream communication, the frequency range for upstream communication has not been expandable by merely increasing the size of the frequency range. Thus, in upstream communication via a common coaxial cable line connected to a plurality of customer premises, if a bigger data-handling capacity was required by the customer premises than the data-handling capacity warranted by the coaxial cable line(s) through the upstream bandwidth between 5 MHz and 42 MHz, conventional methods required either logically splitting the fiber node (i.e. multiplexing multiple upstreams on the fiber return path by TDM, FDM or WDM methods) or an installation of additional coaxial cable lines or an extension of the fiber optic node closer to the customer premises. However, both methods have been costly to implement. Further, while logically splitting the fiber node may solve an equally split node problem, it does not solve an unbalanced node problem.
Thus, a system for stacking signals in an expanded frequency range to transmit additional upstream signals through a coaxial cable line where logically splitting a fiber node may not provide benefit and without necessarily having to install additional coaxial cable lines or extend a fiber optic network closer to customer premises may be useful.